1. Field of the Invention
This invention relates generally to a plastic block apparatus. More particularly, this invention relates to a plastic standoff block that is used to mount a roadway guardrail to an upright support post.
2. Background Art
Conventional standoff blocks are typically composed of plastic or rubber materials and have been approved by the Federal Highway Administration (FHWA) of the U.S. Department of Transportation for mounting steel W-beam type guardrails to steel support posts. These guardrails find extensive use as barriers along roadways to prevent vehicles from veering off the roadway area.
Trinity Industries, Inc. of Dallas Tex., uses an injection molding process to produce one conventional standoff block. The Trinity block is composed of a mixture of recycled material that consists of approximately sixty-seven percent high density polyethylene (HDPE), approximately thirty percent granulated rubber, approximately two percent black color concentrate and approximately one percent, or less, of a blowing agent. This Trinity block has a cavitated or honeycomb-like interior region formed by injection molding constituent materials. Blocks of such compositions, approved for standoff usage, have external dimensions of approximately four inches in.width; approximately 7.3 inches in depth, or horizontal dimension; and, approximately 14 inches in height, or vertical dimension. The rearward, or post, end of the Trinity block includes a horizontal tab-like protrusion projecting rearward from the top edge to overlie a post top thereby enabling the block to be hung from the post substantially vertically during the installation of the W-beam type rail element. The:forward, or rail, face of the block mounting the rail element has a horizontal frontward projecting tab-like protrusion at its bottom edge that underlies the bottom edge of the rail and thereby temporarily supports the rail on the post for ease of installation with conventional through bolts.
Standard guardrail installations, with which the Trinity and other prior art plastic standoff blocks are designed, are required to pass certain high-impact tests approved by the FHWA. The specifics of these tests are available to standoff block manufacturers in published form and FWHA acceptance is based upon the monitored impact resistance of the tested block in a simulated barrier environment.
Because standoff blocks are required to sustain high horizontal directed compressed impact forces, they are molded with cavitated interiors that somewhat resemble a corrugated or honeycomb structure.
It is known to those working in the art of plastic injection molding that both compressive and torque resistance may be accorded rectangular-shaped injection-molded, structures by designing the structure with a honeycomb interior. This interior design is achieved by open-ended cavities formed by the injection molding process. These cavities, which are elongated in the general horizontal direction of the impact forces, are formed by a plurality of elongated, laterally spaced apart interior web-like walls depending at right angles from a common generally planar support base. One example of this type of cavitated structure is disclosed in U.S. Pat. No. 6,071,044, issued to Thomas E. Ricciardelli et al., and is assigned to the same assignee as the instant invention. U.S. Pat. No. 6,071,044 is hereby incorporated by reference in its entirety herein.
Conventional cavitated structures may be molded from virgin or recycled plastic compositions and may be characterized as having an overall U-shaped cross-section; such shape being defined by a pair of laterally spaced apart, parallel exterior side walls and a perpendicular support base or end wall. Thus, the design of conventional cavitated structures is essentially completely U-shaped.
The interior cavities of conventional cavitated structures are formed by injecting molten plastic into a series of parallel, elongated, closed-ended mold cores that extend like fingers from the planar core chambers. The plastic core chambers define the web base and extend perpendicular to the finger-like mold cores. The mold core fingers define the web-like cavity walls and extend forwardly from their base the remaining depth or horizontal dimension of the block. Thus, if the block depth is on the order of seven inches, the mold core fingers might have lengths on the order of six inches each.
A disadvantage of designing a conventional standoff block with a substantially U-shape and a single cavitated interior is that the substantial horizontal dimension of the block requires that the injection molding apparatus have lengthy mold cores for forming the cavity walls. These lengthy mold cores cause the molten plastic material to cool as it is injected into and fills the cores from the base channel. The extremities of the cores forming the open ends of the cavitated structure receive injected plastic at the lowest temperatures, which may be cool enough to cause solidification of the molten plastic before it completely fills the mold core ends. When such plastic solidification occurs before the core ends are completely filled, the web-like interior walls defined by the core will contract, or shrink, more rapidly causing possible deformation of the end product. Thus, a longer flow path will result in increased shrinkage during solidification of the molten plastic material, which may result in cavity walls and their compressive-resistant characteristics being non-uniform and, in some cases, reduced. Such non-uniformity is undesirable from a strength perspective, and moreover, makes the removal of the cavity walls from the mold more difficult.
Therefore, conventional U-shaped cross-section cores, which have relatively long, finger-like sections, cause the compression-resistant characteristics of the structures to be somewhat unpredictable and make the injection-molding process inefficient due to imperfect and/or deformed structures.
It would be desirable, and it is an object of the instant invention, to provide a standoff block design that does not suffer the aforementioned disadvantages of conventional standoff block designs.
The instant invention is directed to a guardrail block for joining a rail section to a vertically disposed support post. The standoff block is molded from plastic material into a substantially H-shaped cross-section, with a horizontal impact resistant cavitated module formed within each U-shaped half of the substantially H-shaped block. Upon installation, the outer.cavitated end of a first module abuts the rail and the outer cavitated end of a second module abuts the post. The inner ends of the modules join to form a vertical central support structure from which plural horizontal exterior struts extend toward the outer ends of the modules to buttress the block against transverse buckling. The struts may project horizontally beyond the post end of the module to straddle, and thereby position, the block on the post.
Accordingly, one embodiment of the instant invention is directed to a standoff block structure for mounting a rail structure of a roadway guardrail to a support post. The block piece mounted there between is composed at least partially of recycled plastic material and including first and second elongated block elements of substantially rectangular cross-sectional shape for providing impact resistance to the guardrail. Each of the block elements has a longitudinal axis, a cored interior formed by longitudinally extending open-ended cavities having open ends thereof at one end of each of the block elements. The open end of the first block element is adapted to abut the rail and the open end of the second block element is adapted to abut the post. The block includes a buttressing structure and a center plate is disposed substantially perpendicularly to the longitudinal axis and interposed between the ends of the block elements opposite the open ends thereof. The center plate joins the opposite ends of the block elements and defines the bottoms of the cavities. At least one bore extends through the block elements and the plate in a direction substantially parallel to the longitudinal axis for receiving a rail mounting fastener.
Another embodiment of the instant invention is directed to a plastic standoff block for mounting a guardrail to an upright support post. The block includes a pair of cavitated-open ended modules for resisting impact forces. Each of the modules is enclosed by a pair of spaced apart, substantially parallel sidewalls and a rearward end wall portion joining the sidewalls to provide a structure of substantially H-shaped cross-section. Each of the modules is further enclosed by respective upper and lower parallel edge walls joined to opposite respective ends of the structure. The sidewalls have a central axis extending there between in a vertical direction and the edge walls have a central axis extending there between in a horizontal direction and intersecting the central, vertically disposed axis at a substantially right angle thereto. A plurality of elongated, vertically spaced-apart interior walls extend from the rearward end wall portion substantially the length of the sidewalls to form the cavitated end of each of the modules, and the rearward end portions are joined together to mount the modules in longitudinal alignment with the cavitated ends thereof and are positioned to face the guardrail and post, respectively.
Yet another embodiment of the instant invention is.directed to a standoff block.molded from plastic material that includes first and second block elements, each block element having a honeycomb interior formed by plural, laterally spaced elongated interior walls having substantially parallel longitudinal axes. The block also includes a support wall interposed between the interior walls perpendicular to the longitudinal axes and joining the first and second block elements in a fixedly aligned relationship.